Multiprotocol Label Switching (MPLS) is a label based switching and forwarding protocol that often results in a very fast lookup of a forwarding table. For example, in an MPLS network, a label is affixed to packets in a customer's traffic. A receiving router or other network device uses the label to make a forwarding decision.
Routers within an MPLS network, such as Label Switched Routers (LSRs), may exchange labels using the Label Distribution Protocol (LDP) and may make forwarding decision in accordance with the Interior Gateway Protocol (IGP). In a large MPLS network, a label switched path (LSP) may be created using the IGP and label information. In scenarios where LDP is used, label information is exchanged between neighboring LSRs. However, these labels are not distributed to other routers in the network. Therefore, the labels are only locally significant to the router that receives and/or sends the label.
In a network that includes multiple hops or segments from the ingress LSR to the egress LSR of the LSP, a broken LSP can present a significant troubleshooting task to an engineer. For example, the engineer must check the routing table and label forwarding table at the ingress and egress LSRs and any LSRs in between. Depending on the size and design of the network, this troubleshooting task can be time consuming and susceptible to errors.